Deletion of <i>Dock7</i> Exons 3 and 4 Results in Reduced Trabecular Microarchitecture and a Decrease in Mineralization

Dedicator of Cytokinesis 7 (DOCK7) has recently emerged as a regulator of skeletal homeostasis, but existing <i>Dock7</i> mutant models harbor only global mutations and are incompatible with tissue-specific deletion studies. We previously generated a <i>Dock7</i>-floxed allele in which exons 3-4 are flanked by LoxP sites. To validate the utility of this allele for future conditional strategies, we globally deleted exons 3-4 to generate <i>Dock7</i> ^{<i>em2/em2</i>} mice and characterized their skeletal phenotype. <i>Dock7</i> ^{<i>em2/em2</i>} mice exhibited a diluted coat color and white belly spot, consistent with spontaneous <i>Dock7</i> mutations. Bone microarchitecture was assessed in 21-week-old males and females. Global deletion of <i>Dock7</i> exons 3-4 resulted in a 30-37% reduction in trabecular bone volume in the distal femur and L5 vertebrae. Cortical bone thickness was unchanged in both sexes; however, male <i>Dock7</i> ^{<i>em2/em2</i>} mice displayed reduced total femoral area, whereas females showed increased medullary area. These data suggest altered appositional bone growth with mutation of <i>Dock7</i>. To assess osteoblast function, bone marrow stromal cells (BMSCs) were differentiated in vitro. <i>Dock7</i> ^{<i>em2/em2</i>} BMSCs exhibited reduced mineralization and decreased <i>Bglap</i> expression, indicating attenuated osteoblast differentiation. These findings demonstrate that <i>Dock7</i> exons 3-4 are required for normal trabecular bone acquisition and osteoblast function. Loss of these exons disrupts DOCK7 activity, supporting the <i>Dock7</i> ^{<i>em2/em2</i>} line as a valid loss-of-function model. The <i>Dock7</i> ^{<i>em2/em2</i>} mouse provides a foundation for future tissue-specific deletion studies to define the cellular roles of DOCK7 in regulating bone formation and trabecular architecture.